Avalanche Forecast

Archived

Apr 8th, 2021–Apr 9th, 2021

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Northwest Coastal.

New snow and strong wind are forming fresh slabs that will likely be reactive to human triggers. Anticipate touchier conditions in wind-drifted areas and dial back terrain where you find more than 25 cm of new snow.

Confidence

Moderate - Forecast precipitation (either snow or rain) amounts are uncertain.

Weather Forecast

Thursday night: Cloudy, 15-25 cm of snow, strong southwest wind, treeline temperatures near -3 C, freezing level near 500 m.

Friday: Mainly cloudy, 5-10 cm of snow, strong southwest wind decreasing to moderate, treeline temperatures -4 C, freezing level near 500 m and dropping to valley bottom overnight.

Saturday: Mix of sun and cloud, isolated light flurries, moderate west wind, treeline temperatures -4 C, freezing level rising to 500 m and dropping to valley bottom overnight.

Sunday: Mix of sun and cloud, light northwest wind, treeline temperatures near -1 C, freezing level rising to 1000 m and dropping to valley bottom overnight.

Avalanche Summary

Since Monday, there have been observations of several large (size 2) storm slabs, numerous small to large (size 1-2) loose wet avalanches, and one instance of a large (size 2) wet slab that failed to the ground from a steep, shallow feature.

Large natural and explosive triggered glide slab avalanche activity has been ongoing for the past few weeks. Glide cracks releasing as full depth glide slab avalanches are extremely difficult to predict. Best practice is to avoid slopes with glide cracks.

Snowpack Summary

An incoming storm is expected to bring 20-30 cm of new snow by Friday afternoon accompanied by strong southwest winds. The new snow will form fresh storm slabs that will likely be more reactive in wind-loaded features.

Cornices are large, looming, and capable of triggering large avalanches when they fail. Previous weak layers are now deeply buried and have not resulted in any recent avalanches. At lower elevations, the new snow is falling on a melt-freeze crust.

Terrain and Travel

Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
Dial back your terrain choices if you are seeing more than 25cm of new snow.
Expect slab conditions to change drastically as you move into wind exposed terrain.
Avoid exposure to slopes that have cornices overhead.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.